Inwardly-opening injection valves, both for direct injection in the high-pressure area and for manifold injection in the low-pressure area, usually have a valve seat in a ball/cone type of construction. That is, at the sealing point formed with the valve seat, the valve needle is configured with a ball or has a spherical form, and the valve seat is conical or hollow frustoconical.
However, in this type of fuel injectors, eccentricities, caused by the manufacturing process, of the seat contact points at the valve needle and at the valve seat often lead to leakages of fuel during operation of the valve.
A fuel injector provided with a spherical closing member is discussed, for example, in the German Patent DE 198 59 484 A1. A fuel injector for high-pressure injection of fuel from a central high-pressure delivery line into combustion chambers of an internal combustion engine has a valve seat, a valve ball and a guide member guiding the valve ball, which for its closure, presses the valve ball onto the valve seat, and for its opening, exposes the valve ball to an initial tension of a spring; the valve ball in the open state is lifted off from the valve seat by a high-pressure jet the valve ball in the open state is lifted off from the valve seat by a high-pressure jet which is supplied via an output throttle bore by a control chamber connected to a central high-pressure delivery line. The valve seat has an approximately steep-walled funnel shape having a right-angled to acute-angled cone angle. Because of the steep-walled funnel shape, the centering of the valve ball is assisted upon closure of the injection control valve, and a radial displacement of the valve ball with respect to a diffuser and the output throttle bore is prevented.
The German Patent DE 103 38 081 A1 discusses a further fuel injector of the type indicated above. In the fuel injector described there, an armature is formed in one piece with a valve needle. Provided in the valve needle are flow-through openings which direct the fuel, flowing through the fuel injector, to a sealing seat. The valve needle is operatively connected by welding to a spherical valve-closure member that, together with a valve-seat member, forms a sealing seat, and downstream of the sealing seat, a spray-orifice disk has formed in it at least one spray-discharge orifice from which fuel is injected into an intake manifold. The inner sealing of the fuel injector with respect to the intake manifold is dependent on the processing when manufacturing the fuel injector. During production of the valve-closure member with the sealing seat formed on it, a high surface quality with a relatively good sealing associated with it is attained by grinding and honing; however, this is qualified by the subsequent processes such as pressing the valve-seat member into the valve sleeve, and the joining of the components by a welded seam.
The above-mentioned fuel injectors having a spherical valve-seat member and hollow frustoconical valve-seat member have the disadvantage that eccentricities of the seat contact points at the valve needle and at the valve seat, caused by the manufacturing process, lead to leakages of fuel during operation.